Lane mark recognition devices are available, including a camera and a radar mounted on a vehicle to recognize lane marks, thus estimating a relative positional relationship between the vehicle and a lane and the curvature indicating the degree of curve of a road. In order to prevent accidents such as lane departure based on this curvature as well as a yaw angle and a lateral position, vehicle controllers are available, performing control such as lane departure alarm and lane departure prevention. According to conventional techniques, a lane departure prevention controller calculates confidence for the overall lane mark recognition result and switches a lane departure control method based on this result on confidence (see Patent Document 1).    Patent Document 1: JP Patent Publication (Kokai) No. 2006-178675 A